Metallic nanofoam electrochemical catalysts and related methods of making and using

Abstract

Catalyst compositions, methods of making a bimetallic nanofoam catalyst composition, and methods of catalyzing a reaction are described. In an example, the catalyst comprises a nanofoam comprising plurality of intertwined nanowires comprising two or more metals. In an example, the nanofoam comprises a three-dimensional interconnected nanonetwork comprising the plurality of intertwined nanowires. In an example, the nanofoam is an aerogel comprising the plurality of intertwined nanowires. In an example, the nanofoam is self-supported, such as where the catalyst composition does not comprise a substrate supporting the nanofoam.

Description

METALLIC NANOFOAM ELECTROCHEMICAL CATALYSTS AND RELATED METHODS OF MAKING AND USINGCROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims the benefit and priority of U. S. Provisional Application No. 63 / 715509, filed on November 1, 2024, and U. S. Provisional Application No. 63 / 819,492, filed June 6, 2025, the entire disclosures of which are disclosed herein in their entireties.BACKGROUND

[0002] With the rapid growth of global energy consumption and the ultimate depletion / limitation of fossil fuels, long-term energy security and environmental sustainability have become the focus of attention. The burning of fossil fuels not only consumes resources but also produces a large amount of greenhouse gases and pollutants, exacerbating climate change and air quality problems. Therefore, the demand for clean, renewable energy has become increasingly urgent. Despite the existence of multiple alternatives, water splitting for hydrogen production has attracted widespread attention as a green and sustainable route, especially when combined with renewable energy.

[0003] One of the most serious bottlenecks in water splitting is the sluggishness of the oxygen evolution reaction (OER), which has a complex four-electron and four-proton coupled electron transfer mechanism. This inherent kinetic bottleneck requires the development of efficient and durable electrocatalysts. IrO2and RuO2, as noble metal oxides, have been standard catalysts due to their high activity, but their high cost and limited supply have hindered their widespread application.

[0004] Efficiency is also limited by the high overpotential required for the catalyst-free hydrogen evolution reaction (HER). Among other HER catalysts, platinum group materials (PGMs) are the best choice for industrial HER catalysis due to their low overpotential, high kinetics, and stability. However, PGMs are expensive and relatively limited in reserves, making them uneconomical for large-scale hydrogen production.

[0005] There is, accordingly, a need for Earth-abundant HER and OER catalysts that can match or even exceed the catalytic activity of PGMs while having excellent economic and durability.SUMMARY

[0006] To address these and related challenges, the present disclosure provides, in various aspects, catalyst compositions, methods of making a bimetallic nanofoam catalyst composition, and methods of catalyzing a reaction.

[0007] In an aspect, the present disclosure provides a catalyst composition comprising a nanofoam comprising plurality of intertwined nanowires comprising two or more metals.

[0008] In an embodiment, the nanofoam comprises a three-dimensional interconnected nanonetwork comprising the plurality of intertwined nanowires.

[0009] In an embodiment, the nanofoam is an aerogel comprising the plurality of intertwined nanowires.

[0010] In an embodiment, the nanofoam is self-supported. In an embodiment, the catalyst composition does not comprise a substrate supporting the nanofoam.

[0011] In an embodiment, the plurality of intertwined nanowires comprises an alloy or solid solution of the two or more metals.

[0012] In an embodiment, the plurality of intertwined nanowires comprises a sintered mixture of the two or more metals.

[0013] In an embodiment, the plurality of intertwined nanowires comprises an un-sintered mixture of the two or more metals.

[0014] In an embodiment, an average pore size of the nanofoam is in a range of about 15 nm to about 80 nm.

[0015] In an embodiment, an average diameter of nanowires of the plurality of nanowires is in a range of about 20 nm to about 60 nm.

[0016] In an embodiment, a Brunauer-Emmett-Teller (BET) surface area of the nanofoam is in a range of about 5 m2 / g to about 25 m2 / g.

[0017] In an embodiment, an electrochemically active surface area (ECSA) of the nanofoam is in a range of about 70 cm2 / g to about 90 cm2 / g.

[0018] In an embodiment, the two or more metals are selected from group consisting of Ni, Sn, and Co.

[0019] In an embodiment, the two or more metals comprise Ni and Sn.

[0020] In an embodiment, a molar ratio of Ni: Sn is in a range of about 1:1 to about 5:1.

[0021] In an embodiment, the plurality of intertwined nanowires comprises a compound NixSny, wherein x is an integer having a value chosen from 4 and 3, and wherein y is an integer having a value chosen from 1-4.

[0022] In an embodiment, the plurality of intertwined nanowires comprises compounds selected from the group consisting of Ni3Sn4, Ni3Sn, Ni3Sn2, Ni4Sn3, and combinations thereof.

[0023] In an embodiment, the two or more metals comprise Ni and Co. In an embodiment, a molar ratio of Ni: Co is in a range of about 1:3 to about 3:1. In an embodiment, the plurality of intertwined nanowires comprises NiCo3.

[0024] In an embodiment, the plurality of intertwined nanowires comprises a phosphide compound of the two or more metals. In an embodiment, the plurality of intertwined nanowires comprises NiCo3P. In an embodiment, nanowires of the plurality of intertwined nanowires comprise surfaces comprising metal-P bonds. In an embodiment, nanowires of the plurality of intertwined nanowires comprise conductive phosphide cores.

[0025] In another aspect, the present disclosure provides a method of making a bimetallic nanofoam catalyst composition. In an embodiment, the method comprises introducing a reducing agent to a solution comprising a first metal source and a second metal source to provide a bimetallic nanofoam comprising a plurality of intertwined nanowires defining a three-dimensional interconnected nanonetwork.

[0026] In an embodiment, the first metal source is selected from NiCl2and Ni(NO3)2and the second metal source is selected from CoCl2and SnCl2.

[0027] In an embodiment, the reducing agent comprises NaBH4.

[0028] In an embodiment, the further comprises removing water from the bimetallic nanofoam, thereby retaining a three-dimensional structure the three-dimensional interconnected nanonetwork. In an embodiment, removing the water from the bimetallic nanofoam comprises freeze drying the bimetallic nanofoam.

[0029] In an embodiment, the method further comprises annealing a mixture of the dried bimetallic nanofoam and a phosphorus source in an inert atmosphere to provide a bimetallic phosphide nanofoam. In an embodiment, the phosphorus source comprises NaH2PO2.

[0030] In an embodiment, a mass ratio of the dried bimetallic nanofoam and the phosphorus source is in a range of about 1:20 to about 1:5.

[0031] In another aspect, the present disclosure provides a method of catalyzing a reaction. In an embodiment, the method comprises contacting a catalytic substrate with a catalyst composition according to any embodiment of the present disclosure, thereby catalyzing a reaction of the substrate.

[0032] In an embodiment, the catalytic substrate comprises water, and wherein the reaction is electrolysis of water. In an embodiment, the water is salt water.

[0033] In an embodiment, the catalyst composition has an overpotential in a range of about 70 mV and about 300 mV measured at 10 mA / cm2.

[0034] In an embodiment, the mass activity of the catalyst composition is in a range of about 200 mA / mg to about 600 mA / mg. In an embodiment, the specific activity of the catalyst composition is in a range of about 0.5 mA / cm2to about 0.8 mA / cm2.

[0035] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.DESCRIPTION OF THE DRAWINGS

[0036] The foregoing aspects and many of the attendant advantages of the subj ect matter of the present disclosure will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

[0037] FIGURE 1A illustrates linear sweep voltammetry (LSV) curves for the hydrogen evolution reaction (HER) on Pt / C and Ni: Co 3:1 (P) catalysts, according to embodiments of the present disclosure;

[0038] FIGURE 1B illustrates LSV curves for the oxygen evolution reaction (OER) on IrO2and Ni:Co 3:1 (P) catalysts, according to embodiments of the present disclosure;

[0039] FIGURES 2A and 2B are (2A) a Tafel diagram of Ni: Co 3: 1 (P) and Pt / C in HER, according to embodiments of the present disclosure, and (2B) a Tafel diagram of Ni:Co 3:1 (P), according to embodiments of the present disclosure, and IrO2in OER;

[0040] FIGURES 3 A and 3B illustrate LSV curves of the (2A) HER and OER (2B) of catalysts according to embodiments of the present disclosure, for the first time and after 5000 cycles;

[0041] FIGURES 4A and 4B illustrate (4A) Chronopotentiometry in HER and (4B) Chronopotentiometry in OER of catalysts according to embodiments of the present disclosure;

[0042] FIGURE 5 A shows the x-ray diffraction (XRD) pattern of Ni3Sn4, S-Ni3Sn4, Ni3Sn, NisS, and Ni4Sn3 aerogels, according to embodiments of the present disclosure;

[0043] FIGURE 5B shows the x-ray photoelectron spectroscopy (XPS) survey spectrum of Ni3Sn4and S- Ni3Sn4aerogels, according to embodiments of the present disclosure;

[0044] FIGURE 5C shows the high-resolution XPS spectra of Ni 2p, according to embodiments of the present disclosure;

[0045] FIGURE 5D shows the high-resolution XPS spectra of Sn 3d, according to embodiments of the present disclosure;

[0046] FIGURE 6 shows the high-resolution XPS spectrum of O Is, according to embodiments of the present disclosure;

[0047] FIGURES 7A-7C show scanning electron microscopy (SEM) and tunneling electron microscopy (TEM) images of Ni3Sn4aerogels, according to embodiments of the present disclosure;

[0048] FIGURES 7D-7F show SEM and TEM images of S- Ni3Sn4aerogels, according to embodiments of the present disclosure;

[0049] FIGURE 8 is a magnified TEM image of S- Ni3Sn4aerogels, according to embodiments of the present disclosure;

[0050] FIGURE 9 is a magnified TEM image of Ni aerogels before aging 12h in water, according to embodiments of the present disclosure;

[0051] FIGURE 10 is a magnified TEM image of Ni aerogels after aging 12h in water, according to embodiments of the present disclosure;

[0052] FIGURES 11A-11D illustrate energy dispersive x-ray spectrometer (EDS) spectrum of Ni, Sn, C, and mixture of S- Ni3Sn4metallic aerogels, according to embodiments of the present disclosure;

[0053] FIGURES 12A and 12B show the energy dispersive x-ray spectra (EDXS) of Ni3Sn4aerogels in different spots, according to embodiments of the present disclosure;

[0054] FIGURES 13A and 13B shows the EDXS of S- Ni3Sn4aerogels in different spots, according to embodiments of the present disclosure;

[0055] FIGURE 14 is a schematic illustration of the formation process for the Ni3Sn4metallic aerogels, according to embodiments of the present disclosure;

[0056] FIGURE 15A is a TEM image of Ni3Sn4aerogels at initial 5s, according to embodiments of the present disclosure;

[0057] FIGURE 15B is a TEM image of Ni3Sn4aerogels at 1 minute, according to embodiments of the present disclosure;

[0058] FIGURE 16A provides LSV curves for HER in 0. IM KOH at 1600 rpm scanned at 10 mV s’1, according to embodiments of the present disclosure;

[0059] FIGURE 16B provides electrochemically active surface areas (ECSA), mass activity (MA), and specific activity (SA) of Ni3Sn4and S- Ni3Sn4at 207 mV overpotential, according to embodiments of the present disclosure;

[0060] FIGURE 16C shows the 6h chronoamperometry test of the Ni3Sn4, S-Ni3Sn4, according to embodiments of the present disclosure, and Pt / C.

[0061] FIGURE 17A provides cyclic voltammograms of Ni3Sn within the range of -1.0 to -0.8 V vs SCE with scan rate from 10mV / s to 100mV / s, according to embodiments of the present disclosure;

[0062] FIGURE 17B provides cyclic voltammograms of Ni3Sn2within the range of -1.0 to -0.8 V vs SCE with scan rate from 10mV / s to 100mV / s, according to embodiments of the present disclosure;

[0063] FIGURE 17C provides cyclic voltammograms of Ni3Sn4within the range of -1.0 to -0.8 V vs SCE with scan rate from 10mV / s to 100mV / s, according to embodiments of the present disclosure;

[0064] FIGURE 17D provides cyclic voltammograms of Ni4Sn3within the range of -1.0 to -0.8 V vs SCE with scan rate from 10mV / s to 100mV / s, according to embodiments of the present disclosure;

[0065] FIGURE 18A illustrates variation of double-layer charging current of Ni3Sn at -0.300 V vs RHE with potential scan rate, according to embodiments of the present disclosure;

[0066] FIGURE 18B illustrates variation of double-layer charging current of Ni3Sn2at -0.300 V vs RHE with potential scan rate, according to embodiments of the present disclosure;

[0067] FIGURE 18C illustrates variation of double-layer charging current of Ni3Sn4at -0.300 V vs RHE with potential scan rate.

[0068] FIGURE 18D shows the variation of double-layer charging current of Ni4Sn3 at -0.300 V vs RHE with potential scan rate, according to embodiments of the present disclosure;

[0069] FIGURE 19A provides Tafel plots for HER in 0.1M KOH at 1600 rpm scanned at 10 mV s’1, according to embodiments of the present disclosure;

[0070] FIGURE 19B provides EIS curves of Ni3Sn4and S- Ni3Sn4at 201 mV overpotential, according to embodiments of the present disclosure;

[0071] FIGURE 19C shows the Turnover Frequency (TOF) of Ni3Sn4and S-Ni3Sn4at 201 mV overpotential, according to embodiments of the present disclosure;

[0072] FIGURE 20 is a schematic diagram of the synthesis route of bimetallic nickel-cobalt phosphide Ni3Co1P, according to embodiments of the present disclosure;

[0073] FIGURES 21A-21K are (21A) an SEM image of Ni3Co1bimetallic aerogel, (21B) SEM image of Ni3Co1bimetallic phosphide (Ni3Co1P), (21C) TEM image of Ni3Co1P, (21D-21G) EDS Mapping of Ni3Co1P, and (21H-21K) EELs Mapping of Ni3Co1P, according to embodiments of the present disclosure;

[0074] FIGURES 22A and 22B provide (22A) XRD pattern of Ni3Co1(22B) XRD pattern of Ni3Co1P, according to embodiments of the present disclosure;

[0075] FIGURES 23A-23D provides (23A) XPS survey spectrum of Ni3Co1P, (23B) High-resolution XPS spectra of Ni 2p, (23C) High-resolution XPS spectra of Co 2p, and (23D) High-resolution XPS spectra of P 2p, according to embodiments of the present disclosure;

[0076] FIGURES 24A and 24B are simulated X-ray absorption near edge structure (XANES) spectra for both Ni3Co1and Ni3Co1P, according to embodiments of the present disclosure;

[0077] FIGURES 25A-25D provide (25A and 25B) Polarization HER curves and Tafel plots of Ni, NiP, Ni3Co1, Ni3Co1P, and Pt / C, and (25C and 25D) ECSA and TOF of Ni, NiP, Ni3Co1, Ni3Co1P, according to embodiments of the present disclosure;

[0078] FIGURE 26A illustrates MA and SA of Ni, NiP, Ni3Co1, according to embodiments of the present disclosure;

[0079] FIGURE 26B illustrates Ni3Co1P. b) Nyquist plots of Ni, NiP, Ni3Co1, and Ni3Co1P derived from EIS measurements, according to embodiments of the present disclosure;

[0080] FIGURES 27A and 27B illustrate (27A) chronopotentiometry of Ni3Co1P. (27B) LSV curves before and after 5000 potential cycles test in 1 m KOH aqueous solution, according to embodiments of the present disclosure;

[0081] FIGURE 28 is a schematic diagram of the synthesis route of bimetallic nickel-cobalt phosphide Ni1Co3P, according to embodiments of the present disclosure;

[0082] FIGURES 29A-29J provide (29A and 29B) SEM images of Ni1Co3and Ni1Co3P, (29C-29E) STEM-ADF imaging of Ni1Co3P, (29F) TEM image of Ni1Co3P, (29G-29J) EDS elemental mapping of Ni1Co3P, according to embodiments of the present disclosure;

[0083] FIGURES 30A-30F provide (30A and 30B) XRD pattern of Ni1Co3and Ni1Co3P, (30C, 30D, 30E) High-resolution XPS spectra of Ni 2p, Co 2p, and P 2p, (30F) N2adsorption–desorption isotherms, according to embodiments of the present disclosure;

[0084] FIGURES 31A-31D provide (31A and 31B) Polarization OER curves and Tafel plots of Co, CoP, Ni1Co3, Ni1Co3P, and IrO2, (31C) ECSA and TOF of Co, CoP, Ni1Co3, and Ni1Co3P, (31D) MA and SA of Co, CoP, Ni1Co3, and Ni1Co3P, according to embodiments of the present disclosure; and

[0085] FIGURES 32A-32C provides (32A) Nyquist plots of Co, CoP, Ni1Co3, and Ni1Co3P derived from EIS measurements, (32B) chronopotentiometry of Ni1Co3P, (32C) LSV curves before and after 5000 potential cycles test in 1 m KOH aqueous solution, according to embodiments of the present disclosure.DETAILED DESCRIPTION

[0086] Described herein are embodiments of catalyst compositions, methods of making a bimetallic nanofoam catalyst composition, and methods of catalyzing a reaction.

[0087] In the following description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the above embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.

[0088] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the presentdisclosure. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0089] Addressing the challenges of off-peak surplus energy and intermittent power from non-dispatchable renewable sources requires efficient and carbon-neutral energy storage and conversion devices. Water splitting, a chemical reaction that separates water into oxygen and hydrogen (2H2O → 2H2+ O2), presents a promising solution by directly converting electrical energy into hydrogen fuel. However, current methods typically demand high energy inputs or rely on expensive platinum group metal (PGM) catalysts. Despite their effectiveness in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) during electrolysis, the high cost and limited sustainability of PGMs hinder their practical applications on a large scale.

[0090] Accordingly, in embodiments, the present disclosure provides non-PGM nanobimetallic, such as nanobimetallic phosphide, catalysts.

[0091] In an embodiment, the present disclosure provides catalyst composition comprising a nanofoam comprising plurality of intertwined nanowires comprising two or more metals.

[0092] As described further herein, in embodiments, such catalysts comprise nickel and cobalt (Ni-Co) (or other pairs of metals), configured to replace traditional platinum (Pt) and iridium (Ir) catalysts. As provided for in the Examples of the present disclosure, the catalysts according to embodiments of the present disclosure exhibit superior catalytic activity and demonstrate enhanced stability, outperforming existing PGM options, and offer a more sustainable and cost-effective solution for large-scale watersplitting applications.

[0093] In embodiments, the bimetallic aerogels, such as bimetallic phosphide aerogels, according to embodiments of the present disclosure comprise nickel (Ni) and cobalt (Co) or tin (Sn) (or any two metals), materials that are abundant on Earth, mixed in a predetermined ratio, and, in embodiments, are doped with phosphorus. As demonstrated further herein, the catalysts according to embodiments of the present disclosure enhance the efficiency of the water decomposition process relative to convention catalysts used for this purpose, such as PGM catalysts. The catalysts according to embodiments of the present disclosure reduce the energy used to initiate the reaction relative to conventional catalystsand improve the efficiency of both the HER and OER, thereby boosting the overall rate of hydrogen production relative to hydrogen production using conventional catalysts. Moreover, the synthesis method for the catalysts of the present disclosure is simple and scalable, and, because it utilizes raw materials that are both abundant and affordable compared to conventional PGM catalysts, they are more sustainable and economically feasible for large-scale applications.

[0094] In embodiments, the bimetallic catalysts according to the present disclosure provide a number of advantageous characteristics. As discussed further herein, in embodiments, the bimetallic catalysts are self-supporting, such as where the bimetallic catalysts of the present disclosure do not include and do not require a substrate or other supporting structure coupled thereto. In this regard, in embodiments, the bimetallic catalysts of the present disclosure eliminate the need for an additional material carrier. This efficiency in design enhances utility of the bimetallic catalysts in various applications.

[0095] In embodiments, the bimetallic catalysts of the present disclosure provide superior performance and durability, such as when compared to conventional catalyst materials. In embodiments, the catalyst materials of the present disclosure provide enhanced catalytic activity compared to PGM catalysts and show remarkable stability under long-term operation. Such performance and durability reduce the necessity for frequent replacements, offering economic and operational advantages.

[0096] As described further herein, in embodiments, the present disclosure provides methods of making bimetallic catalysts, which comprise a slow oxidation process to protect structural integrity of the catalyst material. High-temperature phosphorus doping is carefully managed to prevent or limit structural collapse of the catalyst material. Such methods according to embodiments of the present disclosure are adaptable to various metals, allowing for precise control over oxidation temperature and duration based on the specific oxidation energies of different metals.

[0097] As discussed further herein, the catalyst materials and related methods of making offer versatility in metal selection. This synthesis method is not limited to nickel and cobalt or tin. Rather, the methods of the present disclosure are applicable using a wide range of metals, showcasing their extensive utility in materials science.

[0098] Moreover, the methods and catalyst materials according to embodiments of the present disclosure are suitable with varying and flexible metal ratios, as described further herein. In embodiments, the methods of the present disclosure enable arbitraryadjustments of bimetal ratios, offering precise control over the composition and characteristics of the final product.

[0099] The slow oxidation process of the methods of the present disclosure is adaptable to various metals. Such adaptability allows for the customization of oxidants, as well as adjustments to the oxidation temperature and duration, tailored to the specific oxidation energies of different metals.

[0100] In the HER, as illustrated in FIGURE 1A, the catalyst materials of the present disclosure, here as an example Ni-Co nanobimetallic aerogel phosphide, demonstrate superior catalytic activity. Such catalyst materials require, in embodiments, only 75 mV at a current density of 10 mA / cm2, compared to the 95 mV required by Pt / C. Furthermore, at a higher current density of 100 mA / cm2, in embodiments, the catalyst materials of the present disclosure maintain stronger catalytic activity than Pt / C. In the OER, shown in FIGURE 1B, the catalyst materials of the present disclosure, here as an example, the Ni-Co nanobimetallic aerogel phosphide, exhibits an overpotential of 230 mV at a current density of 10 mA / cm2, which is lower than the 270 mV of commercial IrO2. Even under high current densities, the catalyst materials of the present disclosure continue to outperform commercial IrO2in OER catalytic activity.

[0101] These findings are corroborated by the Tafel diagrams depicted in FIGURE 2. For the HER, the Tafel slope of the Ni: Co 3:1 (P) catalyst shown in FIGURE 2A, as an example, is 101.6 mV per decade, which is slightly lower than the 111.9 mV per decade of commercial Pt / C. In the OER, as seen in FIGURE 2B, the Tafel slope for Ni: Co 3:1 (P) is 92.69 mV per decade, significantly lower than the 132.34 mV per decade observed for commercially available IrO2. These results indicate that the Ni: Co 3:1 (P) catalyst exhibits superior catalytic kinetics in both HER and OER compared to traditional platinum group metal catalysts. The enhanced performance in catalytic kinetics is indicative of why Ni: Co 3: 1 (P) demonstrates high catalytic activity for total water splitting.

[0102] After undergoing 5000 charge-discharge cycles, the activity of the Ni: Co 3:1 (P) catalyst remained virtually unchanged in both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), as shown in FIGURE 3A and FIGURE 3B, respectively. In comparison, many commercial energy storage devices currently on the market are rated for only 2000 cycles. This demonstrates that the Ni: Co 3:1 (P) catalyst maintains exceptionally high activity over the entire service life of most devices, eliminating the need for catalyst replacement during the product’s life cycle.

[0103] Long-term chronopotentiometry tests further validate the durability of the Ni: Co 3:1 (P) catalyst. In the HER reaction, after 45 hours of continuous operation at a current density of 10 mA / cm2, Ni: Co 3:1 (P) retained 98.6% of its initial current response (Figure 4a), surpassing the 95% retention rate of commercial Pt / C. This highlights its exceptional stability and performance. Similarly, in the OER reaction, Ni: Co 3:1 (P) maintained 99.8% of the current response after 45 hours of continuous activity at the same current density, performing better than IrO2, which held 99.0%. These results not only underscore the catalyst’s robustness but also its superior performance over traditional materials in prolonged operational conditions.

[0104] As is shown in the Examples and FIGURES of the present disclosure, these and similar results are shown for other catalyst materials of the present disclosure.

[0105] The catalyst materials of the present disclosure are applicable to several industrially important uses. A few such uses will now be described.

[0106] In an embodiment, the catalyst materials of the present disclosure are configured and otherwise suitable for industrial hydrogen production: In an embodiment, the catalyst material is configured to efficiently split water to produce hydrogen cheaply. In this regard, the catalyst materials according to embodiments of the present disclosure are suitable for large-scale hydrogen production facilities. The efficiency and affordability of the water-splitting capabilities of the catalyst materials of the present disclosure support the expansion of hydrogen as a sustainable energy source.

[0107] In an embodiment, the catalyst materials of the present disclosure are configured and otherwise suitable for renewable energy storage systems. In embodiments, the catalyst materials according to embodiments of the present disclosure are suitable for use and incorporation in energy storage systems, such as to convert and store excess renewable energy in the form of hydrogen. This application enhances the integration of renewable energy sources into the grid, providing a more stable and reliable energy supply.

[0108] In an embodiment, the catalyst materials of the present disclosure are configured and otherwise suitable for fuel cell technology. In an embodiment, the enhanced catalytic activity and stability of the catalyst materials of the present disclosure improve both the efficiency and lifespan of fuel cells relative to those with conventional catalyst materials, such as those comprising PGM. This makes the catalyst materials of the present disclosure particularly valuable for advancing fuel cell technology, and reducing associated costs.

[0109] In an embodiment, the catalyst materials of the present disclosure are configured and otherwise suitable for seawater electrolysis. Due to the robustness and efficiency of the catalyst materials of the present disclosure, the catalysts also supports the electrolysis of seawater to produce hydrogen. This application could revolutionize hydrogen production by utilizing the abundant resource of seawater, significantly expanding potential hydrogen sources.

[0110] As above, in an embodiment, the present disclosure provides a catalyst composition comprising a nanofoam comprising plurality of intertwined nanowires comprising two or more metals. In an embodiment, the nanofoam is a bimetallic catalyst composition defining a plurality of pores comprising pores having one or more dimensions on a nanometer scale, such as less than 1 micron.

[0111] In an embodiment, the nanofoam comprises a three-dimensional interconnected nanonetwork comprising the plurality of intertwined nanowires. In an embodiment, the three-dimensional interconnected network comprises nanowires, such as wires comprising the bimetallic compositions described herein, extending variously in three dimensions, such as three orthogonal dimensions. In an embodiment and as discussed further herein, in embodiments, the nanowires comprise diameters or other thickness dimensions of less than 1 micron. In embodiments, the nanowires form or otherwise define an interconnected or enmeshed network of nanowires.

[0112] In an embodiment, the nanofoam is an aerogel comprising the plurality of intertwined nanowires.

[0113] In an embodiment, the nanofoam is self-supported. In this regard, in embodiments and as described herein, in embodiments, the catalyst composition does not comprise a substrate or other structure supporting the nanofoam or to which the catalyst composition is coupled, such as for structural support.

[0114] In embodiments, the catalyst material can comprise a number of different metal forms, crystalline and amorphous, sintered and un-sintered. Accordingly, in an embodiment, the plurality of intertwined nanowires comprises an alloy or solid solution of the two or more metals. In an embodiment, the plurality of intertwined nanowires comprises a sintered mixture of the two or more metals. In an embodiment, the plurality of intertwined nanowires comprises an un-sintered mixture of the two or more metals.

[0115] As above, in an embodiment, the catalyst materials of the present disclosure can define a nanofoam and / or aerogel comprising a plurality of pores havingnanoscale dimensions. In an embodiment, an average pore size of the nanofoam is in a range of about 15 nm to about 80 nm, such as in a range of about 25 nm to about 50 nm. Without wishing to be bound by any particular theory, it is believed that pores smaller than 15 nm increase resistance; whereas those larger than 80 nm reduce active-site density. The noted ranges, such as about 25 nm to about 50 nm mesopore range enhances a balance between ion diffusion and active-site accessibility, contributing to improved turnover frequency and stability in alkaline media.

[0116] As provided further herein, scanning electron microscopy (SEM) and nitrogen adsorption-desorption measurements show that, for example, both Ni1Co3P and Ni3Sn4P aerogels exhibit 3D porous networks with mesopores predominantly between 20-60 nm. Additionally, as also provided further herein, for Ni-Co-P, the interconnected pores (-30-50 nm) facilitate electrolyte penetration and mass transport during OER / HER, while maintaining mechanical integrity.

[0117] In an embodiment, an average diameter of nanowires of the plurality of nanowires is in a range of about 20 nm to about 60 nm, such as in a range of about 30 nm to about 50 nm. Without wishing to be bound by any particular theory, it is understood that such nanowire diameters, such as in a range of about 30 nm to about 50 nm allow relatively uniform current distribution and reduce internal Ohmic losses, enhancing both catalytic efficiency and structural robustness. These diameters provide sufficient electronconduction pathways while preventing mechanical collapse during long-term operation.

[0118] As provided further herein, tunneling electron microscopy (TEM) images reveal that, for example, the Ni-Co and Ni-Sn frameworks are comprising interwoven nanowires of about 30 nm to about 50 nm in diameter, maintain structural continuity, such as even after phosphidation.

[0119] In an embodiment, a Brunauer-Emmett-Teller (BET) surface area of the nanofoam is in a range of about 5 m2 / g to about 25 m2 / g, such as in a range of about 8 m2 / g to about 23 m2 / g. Within such ranges, such as in a range of about 8 m2 / g to about 23 m2 / g, the catalyst materials of the present disclosure maintain advantageous electronic conductivity and mechanical stability while providing adequate exposed active sites. Without wishing to be bound by any particular theory, it is understood that the limited surface-area increase supports that the observed activity improvement originates primarily from electronic modulation rather than morphological changes.

[0120] As described further herein, the Ni1Co3P aerogel exhibits a slight increase in BET surface area from 5.78 m2g−1to 8.82 m2g−1after phosphidation, demonstrating that the phosphorus introduction preserves the 3D nanonetwork structure with minimal morphological alteration. Further, Ni3Co1P shows a comparable trend, with its surface area increasing from 21.23 m2g−1to 22.96 m2g−1confirming that both Ni-Co-P systems exhibit only minor porosity changes (< 15%) upon phosphidation.

[0121] In an embodiment, an electrochemically active surface area (ECSA) of the nanofoam is in a range of about 70 cm2 / g to about 90 cm2 / g, such as in a range of about 75 cm2 / g to about 85 cm2 / g. Within such ranges, such as in a range of about 75 cm2 / g to about 85 cm2 / g, the nanofoam achieves an advantageous balance between active-site density and electronic conductivity, enabling superior catalytic activity with excellent mechanical robustness and structural retention after long-term OER / HER cycling.

[0122] Further, values below 70 cm2 / g correspond to incomplete phosphidation or structural collapse, leading to limited accessible sites. Additionally, values above 90 cm2 / g are typically associated with over-porous or unstable frameworks, reducing electrical conductivity and long-term durability.

[0123] As shown further herein, across tested bimetallic phosphide nanofoams, such as Ni1Co3P, Ni3Co1P, Ni3Sn4P, the ECSA values fall between 70-90 cm2 / g.

[0124] The moderate increase (-10-15%) after phosphidation suggests that while additional surface sites are generated, the catalytic enhancement primarily arises from electronic effects (phosphorus-induced charge redistribution) rather than drastic surfacearea expansion.

[0125] In an embodiment, wherein the two or more metals are selected from group consisting of Ni, Sn, and Co. In an embodiment, the two or more metals comprise Ni and Sn. In an embodiment, a molar ratio of Ni: Sn is in a range of about 1:1 to about 5:1, such as in a range of about 3:1 to about 4:1. In embodiments, within 1: 1— 5: 1, the Ni-Sn alloy network retains a continuous metallic framework and balanced electronic structure. In embodiments, the Ni-rich range (3: 1-4: 1) provides enhanced charge transfer and active site exposure, leading to superior catalytic performance and durability.

[0126] As shown further herein, x-ray diffraction (XRD) and TEM analysis confirm that when Ni: Sn ratio is between 1: 1 and 5:1, crystalline bimetallic phases such as Ni3Sn2, Ni3Sn4, and Ni4Sn3are formed. Excellent OER / HER performance occurs at Ni: Sn≈ 3:4 (Ni3Sn4), corresponding to a moderately Ni-rich phase with high conductivity and stable Ni-P bonding after phosphidation.

[0127] When Ni: Sn < 1:1, amorphous Sn-rich phases dominate and lose catalytic stability; when Ni: Sn > 5: 1, the system transitions toward monometallic Ni3P or Ni2P.

[0128] In an embodiment, the plurality of intertwined nanowires comprises a compound NixSny, wherein x is an integer having a value chosen from 4 and 3, and wherein y is an integer having a value chosen from 1-4. In an embodiment,

[0129] In an embodiment, the plurality of intertwined nanowires comprises compounds selected from the group consisting of Ni3Sn4, Ni3Sn, Ni3Sn2, Ni4Sn3, and combinations thereof.

[0130] In an embodiment, the two or more metals comprise Ni and Co. In an embodiment, a molar ratio of Ni: Co is in a range of about 1:3 to about 3:1, such as in a range of about 1:2 to about 2:1. When the ratio falls outside 1:3 - 3: 1 (e.g., < 1:3 or > 3: 1), phase segregation occurs, forming Co-rich (CoP / Co2P) or Ni-rich (Ni2P / Ni3P) domains. These single-metal-dominated phases exhibit inferior conductivity, stability, and bifunctional catalytic activity.

[0131] This range is experimentally supported further herein by the synthesis and characterization of the Ni-Co-P nanofoam catalysts (Ni1Co3P, Ni3Co1P, and NiCo-P). Within this window, phosphidation yields a homogeneous bimetallic phosphide network primarily composed of orthorhombic Ni2P with minor NiCoP phases. These compositions exhibit strong Ni-Co electronic coupling, optimized d-band alignment, and high electrochemical performance — including low overpotentials (-75-90 mV for HER and -210-240 mV for OER) and large electrochemically active surface areas (ECSA - 75-85 cm2g-1).

[0132] Thus, the experimentally validated range of 1:3 to 3:1, and especially 1:2 to 2:1, reflects the compositional region that maintains Ni-Co co-phosphide homogeneity and delivers the advantageous synergistic electronic configuration for superior catalytic performance.

[0133] In an embodiment, the plurality of intertwined nanowires comprises NiCo3.

[0134] In an embodiment, the plurality of intertwined nanowires comprises a phosphide compound of the two or more metals. In an embodiment, the plurality of intertwined nanowires comprises NiCo3P. In an embodiment, nanowires of the plurality ofintertwined nanowires comprise surfaces comprising metal-P bonds. In an embodiment, nanowires of the plurality of intertwined nanowires comprise conductive phosphide cores. METHODS

[0135] In an aspect, the present disclosure provides methods for making a catalyst composition according to embodiments of the present disclosure. In an embodiment, the method comprises introducing a reducing agent to a solution comprising a first metal source and a second metal source to provide a bimetallic nanofoam comprising a plurality of intertwined nanowires defining a three-dimensional interconnected nanonetwork.

[0136] The methods of the present disclosure are versatile and can include synthesis phosphides of any two transition metals.

[0137] In an embodiment, the first metal source is selected from NiCl2and Ni(NO3)2and the second metal source is selected from CoCl2and SnCl2.

[0138] In an embodiment, the reducing agent comprises NaBH4.

[0139] In an embodiment, the method comprises removing water from the bimetallic nanofoam, thereby retaining a three-dimensional structure the three-dimensional interconnected nanonetwork.

[0140] In an embodiment, removing the water from the bimetallic nanofoam comprises freeze drying the bimetallic nanofoam.

[0141] In an embodiment, the method comprises annealing a mixture of the dried bimetallic nanofoam and a phosphorus source in an inert atmosphere to provide a bimetallic phosphide nanofoam. In an embodiment, the phosphorus source comprises NaH2PO2.

[0142] In an embodiment, a mass ratio of the dried bimetallic nanofoam and the phosphorus source is in a range of about 1:20 to about 1:5, such as in a range of about 1:15 to about 1:8. In such ranges, a sufficient excess of phosphorus precursor ensures complete phosphidation of the Ni-Co or Ni-Sn bimetallic nanofoam. When the ratio approaches 1:20, the system is phosphorus-rich, favoring full conversion and uniform P incorporation across the 3D nanofoam network. However, excessively high phosphorus levels can cause local over-reduction and partial collapse of the porous structure. Conversely, when the ratio approaches 1:5, phosphidation becomes phosphorus-deficient, leading to incomplete transformation and the presence of residual metallic or oxide species.

[0143] Therefore, maintaining the mass ratio within 1:20-1:5, and preferably around 1:15-1:8, provides optimal phosphorus activity, balancing complete conversion with structural integrity and high electrocatalytic performance.

[0144] An embodiment of the methods of the present disclosure comprising Ni-Co bimetallic combination, such as according to Examples 2 and 3 will be described. While a method for preparing a bimetallic Ni-Co phosphide catalyst is described, it will be understood that other methods, such as those for preparing Ni-Sn bimetallic catalysts and other bimetallic catalysts are possible and within the scope of the present disclosure.

[0145] Such a catalyst comprises a Ni-Co bimetallic nano-aerogel. In an embodiment, this base material leverages a Ni-Co bimetallic nano-aerogel structure to provide multiple active sites and maximize surface area, crucial for enhancing catalytic efficiency. As above, in an embodiment, the method comprises phosphorus doping of the bimetallic nanoaerogel. In an embodiment, the catalytic activity and durability are significantly improved through phosphorus doping.

[0146] In an embodiment, the synthesis of the Ni-Co bimetallic nano-aerogel comprises a controlled oxidation process followed by phosphorus doping. In embodiments, this method is used to protect the material’s structure, increase its conductivity and promote faster electron transfer, enhancing the overall catalytic performance.

[0147] In an embodiment, the Ni-Co bimetallic nano-aerogel phosphide operates effectively under alkaline conditions. Structure and function of the catalyst are illustrated and described Examples 2 and 3 of the present disclosure.

[0148] In an embodiment, or the catalyst synthesis, a total of 6 mmol of Ni and Co precursors are used, specifically NiCl2·6H2O and CoCl2·6H2O, mixed in a molar ratio of 1:3 (The precursor solution comprised 1.5 ml of 1M NiCl2·6H2O and 4.5 ml of 1M CoCl2·6H2O, totaling 6 ml).

[0149] Both precursors are dissolved in 14 ml of water, stirring for 5 minutes to ensure a homogeneous distribution and complete dispersion.

[0150] 200 mL of a 0.3 M solution of sodium borohydride (NaBH4) is prepared.

[0151] The precursor solution is quickly and evenly added to the NaBH4solution, ensuring thorough mixing. The mixture is then stirred continuously for 10 minutes to promote a complete reaction and uniform distribution of the components.

[0152] After the reaction, black solid formed is collected. The collected solid is rinsed thoroughly with a 1: 1 mixture of ethanol and water to remove any impurities or unreacted materials. This cleaning step helps ensure the purity of the final product.

[0153] The washed solids are immediately frozen by placing them in a -80°C freezer for 2 hours. Following this, the frozen solids are thoroughly dried using a freeze-drying process. This careful freeze-drying ensures that the structural integrity of the material is maintained while removing all moisture. The result is the production of Ni-Co bimetallic aerogel, a highly porous and effective catalyst.

[0154] After preparation, 5 ml of water was meticulously injected into the Ni-Co bimetallic aerogel. The samples are then placed in an oven and subjected to a slow oxidation process at a controlled temperature of 85°C for six hours. This gradual oxidation is for stabilizing the structure of the aerogel. This step represents a key innovation in this synthesis method.

[0155] After six hours, the water injected into the Ni-Co bimetallic aerogel has completely evaporated. The oxidized aerogel is then thoroughly mixed with sodium hypophosphite monohydrate, using a mass mixing ratio of 1:10. This step integrates the phosphorus source uniformly throughout the aerogel, for the subsequent doping process.

[0156] The prepared sample is transferred to a tube furnace within the reactor. The reactor was programmed to heat the sample to 350°C at a rate of 11 °C per minute under a nitrogen flow of 100 standard cubic centimeters per minute (seem). Nitrogen, serving as a protective gas, does not participate in the reaction but ensures an inert atmosphere to facilitate the formation of phosphide. The sample is maintained at this temperature for two hours to complete the phosphide formation reaction.

[0157] After the reaction phase, the sample was allowed to cool to room temperature. It was then thoroughly washed with a 1: 1 mixture of water and ethanol to remove any residues or unreacted materials. Following the wash, the sample was dried in an oven set at 85°C.

[0158] In another aspect, the present disclosure provides a method of catalyzing a reaction. In an embodiment, the method comprises contacting a catalytic substrate with a catalyst composition according to any embodiment of the present disclosure, thereby catalyzing a reaction of the substrate.

[0159] In an embodiment, the catalytic substrate comprises water, and wherein the reaction is electrolysis of water. In an embodiment, the water is salt water, such as sea water.

[0160] In an embodiment, the catalyst composition has an overpotential in a range of about 70 mV and about 300 mV measured at 10 mA / cm2, such as in a range of about 75 mV to about 210 mV.

[0161] As demonstrated further herein, the catalyst compositions of the present disclosure, such as the optimized Ni1Co3P catalyst, exhibit an OER overpotential of 208 mV at 10 mA cm2, while the corresponding HER overpotential is -75-85 mV under identical alkaline conditions (1.0 M KOH). Other Ni-Co and Ni-Sn-P compositions show similar activity within this range. Overpotentials below 70 mV are uncommon for nonprecious-metal catalysts, while values above 300 mV indicate poor electronic coupling or insufficient active site utilization. The disclosed ranges of overpotentials, therefore, reflect the experimentally validated window where the catalysts exhibit excellent bifunctional performance and stability.

[0162] In an embodiment, the mass activity of the catalyst composition is in a range of about 200 mA / mg to about 600 mA / mg, such as in a range of about 300 mA / g to about 500 mA / g. Such ranges are shown further herein in the measured activity of, for example, the Ni1Co3P and Ni3Sn4P nanofoam catalysts, which display mass activities of -360-470 mA mg1at p = 200 mV (OER) and -280-350 mA mg1at p = 100 mV (HER). These values reflect the high intrinsic activity of the P-induced electronic reconfiguration while maintaining moderate catalyst loading (~1 mg cm−2). Mass activities below 200 mA mg−1generally result from incomplete phosphidation or poor conductivity, while exceeding 600 mA mg−1typically indicates instability or inaccurate normalization.

[0163] In an embodiment, the specific activity of the catalyst composition is in a range of about 0.5 mA / cm2to about 0.8 mA / cm2, such as in a range of about 0.55 mA / cm2to about 0.75 mA / cm2.

[0164] As shown further herein, the experimental data show that, for example, the Ni1Co3P nanofoam exhibits a specific activity of -0.63 mA cm2, consistent with enhanced electronic conductivity and optimized Ni-Co synergistic interaction. This range reflects the effective balance between active-site density and charge-transfer efficiency. Values below 0.5 mA cm−2correspond to underactive or partially oxidized surfaces, while those above 0.8 mA cm−2are typically observed only in transient or unstable systems. EXAMPLES EXAMPLE 1: NIXSNY AEROGELS

[0165] The present Example describes sintered and unsintered NixSnyaerogels with various ratios of Ni and Sn (x:y) suitable for use as catalysts for electrolytic hydrogen generation in the hydrogen evolution reaction (HER). In the embodiments herein, the composition of the catalyst used, as an example, includes Ni3Sn4aerogels. Such aerogelswere obtained by a facile reduction process, in which Ni(NO3)2·6H2O and SnCl2solution were directly injected into a NaBH4 solution under stirring conditions. It is to be noted that the concentration of two reductants and feeding salts has an important impact on the crystallinity and the chemical compositions of Ni3Sn4aerogels. Inductively coupled plasma mass spectrometry (ICP-MS) shows that the ratio of the elements of aerogels are roughly the same as the feeding ratio of precursors, indicating the successful control of the chemical component by varying the feeding ratio of precursor salts.

[0166] FIGURE 5 A shows the X-ray diffraction (XRD) patterns of NixSny. It is to be appreciated that characteristic peaks of aerogels shown in FIGURE 5A vary with different elemental compositions. As known by the standard diffraction powder fraction (PDF) cards, the peaks at 30.19°, 33.07° and 43.02° of obtained Ni3Sn4and S- Ni3Sn4aerogels, as shown in FIGURE 5A, are attributed to the (101), (113), (110) lattice of Ni3Sn4alloys. The peaks of Ni3Sn4between 50° and 60° are ascribed to the impurity phase of Ni and Sn oxide, including a multiphase existing in the material. However, as the heat treatment is applied, those peaks are largely diminished, suggesting a high purity and well obtained Ni3Sn4alloy phase.

[0167] The surface composition and chemical state of the resulting aerogels are thoroughly investigated by X-ray photoelectron spectroscopy (XPS). FIGURE 5B shows the representative XPS survey scan spectrum and indicates the existence of Ni and Sn elements, which is consistent with the results of ICP-MS. As can be seen in FIGURE 5C, the high-resolution spectrum of Ni 2p for S- Ni3Sn4aerogels can be further deconvoluted into four main peaks of metallic Ni (852 and 868 eV) with two satellite peaks at 862 eV. The ratio of Ni / Ni2+calculated by comparing the relative peak area is 0.23, which is lower than the S- Ni3Sn4aerogels after sintering. It appears that the sintering process in an inert atmosphere induced a change of the Ni chemical status from Ni2+to Ni°.

[0168] The XPS spectra of as, shown in FIGURE 5D, mainly exhibits peaks for two Sn valence states. The peaks at 486 and 494 eV are related to Sn2+valence state, SnO. The second component at 483 and 491.5 eV can be ascribed to a reduced, Sn° state. After sintering, the XPS spectra changed, since the migration of oxygen took place, as was expected in an inert atmosphere. Therefore, only the Sn2+spectral line is present. In the corresponding O ls spectrum, as shown in FIGURE 6, the peak at 532.9 eV is ascribed to v, while the peaks at 530.1 and 531.7 eV are attributed to lattice oxygen sites and absorbed surface, respectively.

[0169] The morphology of the as-prepared aerogel has been specifically revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The SEM and TEM images of the Ni3Sn4aerogel show the formation of a 3D porous structure as shown in FIGURES 7A-7C, constructed by nanowires with inconsistent diameters. In the example embodiments herein, those nanowires are intertwined and fused at random positions to form a porous structure with open pores and wide pore size distribution. The TEM image of Ni3Sn4aerogels after sintering is also shown in FIGURES 7D-7F and exhibits a similar 3D porous morphology to Ni3Sn4aerogels, suggesting a robust structure against elevated heating.

[0170] In particular embodiments, the average diameter of the nanowires, e.g., S-Ni3Sn4aerogels, ranges from 20-60 nm, as shown in FIGURE 8. In comparison, the Ni aerogel in FIGURE 9 presents a porous nanowire network with an average nanowire diameter of 35 nm, while later it changed into flake morphology in less than 12 hours as shown in FIGURE 10. The elemental compositions of the S-Ni3Sn4aerogels were investigated by energy-dispersed X-ray spectroscopy (EDXS). EDXS results are in good agreement with the results from XPS. The EDXS elemental mapping in SEM shown in FIGURES 11A-11D represents the elements Ni and Sn are uniformly distributed in the micrometer scale, and the ratio of Ni and Sn is in agreement with the molar ratio of Ni and Sn precursors. The EDXS spot analysis of Ni3Sn4shown in FIGURE 12 in a different area, shows a variety of the Ni and Sn ratio, which is possibly a consequence of the formation of moieties with increased Ni or Sn content, indicating Ni and Sn are not well alloyed before sintering, as it is shown in XRD pattern. After sintering, the EDXS spot analysis from the random area shown in FIGURE 13 shows consistency in the element ratio of Ni and Sn, suggesting a well-obtained alloy statue. The improvement of HER activity may be related to such a well-obtained alloy structure.

[0171] The as-obtained hydrogel floated in the solution, driven by the generated H2 bubbles from NaBH4 inside the gel networks during the gelation process. Generally, the NaBH4-to-metal-salt ratio (R / M) is set to 5.0, wherein an excessive amount of NaBH4 (R / M = 100) was adopted. The ex-situ transmission electron microscopy (TEM) revealed the fast development of the branched-nanowire network at different time scales, as represented by FIGURE 14. In the first few seconds, metal precursors were reduced by NaBH4 into nanoparticles and followed by the change of the apparent solution to black suspension.

[0172] The size of these nanoparticles reached several nanometers and increased to several micrometers in the next 10 minutes. Meantime, the growth of the average ligand size from a few nanometers to 30.7 nm was also observed as represented in FIGURES 15A and 15B. The observation of the nanochain-like ligand and nanoparticles in 10 minutes is consistent with the formation and growth of ligand from nanoparticles proceed spontaneously in the first few minutes. Unlike the usual formation of bulk gels, a nearly immediate occurrence of the gel piece from the bulk solution is observed, which is ascribed to the disturbance of H2 bubbles from an excessive amount of NaBH4due to selfdecomposition. To this end, the gelation time was considerably shortened. Moreover, with precise control of the amount of NaBH4, a heating-involved two-step gelation process is achievable, where NaBH4promotes the gelation process of the precursor solution.

[0173] The HER performance of NixSnyaerogels was assessed with S-Ni3Sn4, S-Ni3Sn4, Ni, Sn, and commercial Pt / C electrocatalyst in a standard three-electrode system with 1.0 M KOH as the electrolyte. FIGURE 16A shows the HER polarization curves tested by linear scan voltammetry and compensated with a 95% IR drop. Notably, S-NisS requires low overpotentials of 207 mV to reach 10 mA cm’2, superior to those of Ni, Sn and Ni3Sn4(E10= 238 mV). A similar trend can also be observed in the HER polarization curved before the IR drop.

[0174] To measure the quantity of catalytically active sites in the as-prepared Ni3Sn4aerogels, the electrochemically active surface areas (ECSA) are calculated based on the double-layer specific capacitance, as shown in FIGURE 17 and FIGURE 18. Ni3Sn4gives a higher ECSA of 5.2 cm2in comparison with those of S-Ni3Sn4(3.6 cm2), revealing that the aerogel porous structure can present more catalytic sites and the heating process may slightly reduce the surface area of the aerogels as represented by FIGURE 16B.

[0175] The corresponding results of mass activities (MA) and specific activities (SA) are also shown in FIGURE 16B. A trend is obtained for these two indicators, implying that S-Ni3Sn4gives the MA and SA values of 61.3 mA / mg and 0.7 mA / cm2, higher than that of Ni3Sn4(25.8 mA / mg and 0.2 mA / cm2), which means that S-Ni3Sn4possesses highest intrinsic activities to acquire excellent HER kinetics. The evaluation of catalytic stability for electrocatalysis is another important indicator for HER performance.

[0176] The chronopotentiometry results of both Ni3Sn4and S-Ni3Sn4represented in FIGURE 16C, recorded at 10 mA cm2for 10 h in N2-saturated 1.0 M KOH, showed parallel trends without a visible potential drop, suggesting good sustainability. However,the Pt / C with same loading exhibit a high decay of activity in the first few hours, further demonstrating the improved stability of the S-Ni3Sn4catalyst relative to PGM catalysts, such as Pt / C.

[0177] To deeply understand the conspicuous catalytic activity of S-Ni3Sn4, the kinetic features of the resulting S-Ni3Sn4is 84.8 mV dec-1, lower than that of Ni3Sn4(97.2 mV dec-1), revealing the higher response rate of catalytic current with the increase of overpotentials, as shown in FIGURE 19A. Besides, the obtained Tafel slope (i.e., the relation to the activation energy of the reaction) of S-NisS is the same as the one of Pt / C, suggesting similar reaction steps for the two materials. Further kinetic assessment was performed using electrochemical impedance spectroscopy (EIS) represented in FIGURE 19B. The corresponding Nyquist plots were composed of high and low-frequency responses, which are respectively ascribed to the solution resistance (Rs) and interfacial charge transfer resistance (Ret) in the HER. After sintering, the Ret of S-Ni3Sn4decreased, manifesting a higher charge transfer efficiency after sintering.

[0178] FIGURE 19C provides a comparison of turning-over frequency among S-Ni3Sn4, Ni3Sn4, Ni and Sn, implying S-Ni3Sn4gives the highest value of 2.573 s-1, almost 3 times better than that of Ni3Sn4. Surprisingly and unexpectedly, this demonstrates that S-Ni3Sn4has improved intrinsic activities after heat treatment to access excellent HER kinetics.EXAMPLE 2: BIMETALLIC PHOSPHIDE NANOFOAM CATALYSTS FOR WATER SPLITTING HER

[0179] The present Example demonstrates hydrogen evolution reaction (HER) using bimetallic nanofoam catalysts according to embodiments of the present disclosure, including nickel-cobalt bimetallic phosphide.

[0180] The present Example provides a support-free Ni-Co bimetallic phosphide aerogel that is an efficient and durable HER electrocatalyst in alkaline conditions. The material is synthesized via a facile two-step process: rapid NaBH4 reduction of Ni2+ / Co2+to form a 3D bimetallic nanofoam, followed by thermal phosphidation using sodium hypophosphite. This template-free approach produces a self-standing porous network of Ni-Co-P without the need for conductive supports or binders is suitable for scalable fabrication. Comprehensive studies comparing Ni-only, Ni-P, Ni-Co alloy, and Ni-Co-P catalysts revealed the critical role of phosphorus doping and bimetallic synergy in enhancing HER performance. Ni-Co-P (3:1) emerged as an advantageous composition,achieving a low overpotential of 75 mV at 10 mA cm2and a Tafel slope of -101.6 mV dec1in 1 M KOH - metrics that outperform not only its monometallic or non-phosphidated counterparts but even a commercial Pt / C catalyst under the same conditions. The Ni-Co-P aerogel’s excellent activity is attributed to its enlarged electrochemical surface area (from the 3D porous architecture), the intrinsic catalytic synergy of Ni and Co sites, and the presence of Ni / Co-P bonds that optimally balance hydrogen adsorption energies. Equally important, the Ni-Co-P catalyst demonstrated outstanding durability, retaining -97% of its HER current over 45 hours at 10 mA cm2with negligible degradation, far surpassing the stability of typical noble-metal catalysts in alkaline media. This durability arises from the robust Ni-Co-P framework and the self-passivating nature of phosphides which resist corrosion. Collectively, these favorable properties render the Ni-Co 3: 1 phosphide aerogel a highly efficient catalyst for sustainable hydrogen production. The insights gained from the present Example include, for example, that combining bimetallic alloying with heteroatom (P) incorporation in a 3D nanostructured matrix can produce synergistic effects, provide next-generation electrocatalysts for water splitting and other energy conversion technologies. The efficient and stable Ni-Co-P aerogel demonstrated in the present Example provide replacements for precious metals in alkaline electrolyzers, thereby reducing costs and improving the viability of green hydrogen as a clean energy carrier.

[0181] Materials and Reagents

[0182] Nickel(II) chloride hexahydrate (NiCl2·6H2O, ≥98%), cobalt(II) chloride hexahydrate (CoCl2·6H2O, ≥98%), sodium borohydride (NaBH4, powder, ≥98%), sodium hypophosphite monohydrate (NaH2PO2·H2O, ≥99%), and Nafion® 5 wt% solution were purchased from Sigma-Aldrich or Thermo Fisher and used as received. Commercial 20 wt% Pt on carbon black (Pt / C) was obtained from Sigma-Aldrich for benchmarking. Potassium hydroxide (KOH, pellet, >85%) was from Amresco. Ethanol (200 proof) was from J. T. Baker. Ultrapure deionized water (18.2 MQ cm) was produced by a Millipore Milli-Q system.

[0183] Catalyst Synthesis

[0184] Synthesis of Ni-Co Bimetallic Aerogels

[0185] Ni-Co alloy aerogels were prepared by rapid chemical reduction. A 3:1 molar ratio of NiCl2·6H2O and CoCl2·6H2O (total 6 mmol) was dissolved in 14 mL of water. After stirring, the solution was injected into 200 mL of 0.3 M NaBH4under vigorousstirring. The reduction proceeded for 10 minutes. The black Ni-Co gel was collected, washed thoroughly with water and ethanol, and freeze-dried to yield a monolithic aerogel.

[0186] Synthesis of Ni-Co Phosphide Aerogels

[0187] The dried aerogel (-100 mg) was pre-oxidized by adding 5 mL water and drying at 85 °C in air for 6 h. It was then mixed with NaH2PO2·H2O (1:10 mass ratio), placed in a porcelain boat, and annealed at 350 °C under N2 flow for 2 h. After cooling, the product was washed with water and ethanol and dried at 85 °C, yielding Ni-Co-P aerogels.

[0188] Electrochemical Measurements

[0189] For the HER, the overpotential (q) was calculated from the LSV curve as:

[0190] q = E(RHE) - 0.00 V

[0191] where E(RHE) is the potential at 10 mA cm2vs. RHE. This reflects the extra voltage required to drive the HER beyond the thermodynamic equilibrium potential of 0 V.

[0192] Electrocatalytic overpotential (q) was calculated from the LSV curves at a fixed current density of 10 mA cm2using the equation:

[0193] q = E(RHE) - 1.23 V

[0194] where E(RHE) is the measured potential converted from Hg / HgO reference according to: E(RHE) = E(Hg / HgO) + 0.098 + 0.059 x pH.

[0195] E(RHE) = E(Hg / HgO) + 0.098 + 0.059 x pH

[0196] LSV was recorded at 5 mV s1with 1600 rpm rotation speed. EIS was measured at the overpotential of 200 mV with 5 mV amplitude from 100 kHz to 0.01 Hz. Chronopotentiometry was performed at 10 mA cm2for long-term stability.

[0197] Electrochemical Surface Area (ECSA)

[0198] The ECSA was evaluated using the electrochemical double-layer capacitance (C_dl), determined from cyclic voltammetry in a non-faradaic potential region (0.875-0.975 V vs. RHE) at scan rates ranging from 20 to 100 mV s '. The current density difference (Aj = ja - jc) at 0.925 V was plotted against scan rate, and the slope was equal to 2 x C_dl. The ECSA was calculated by:

[0199] ECSA = C_dl / C_s (C_s = 0.040 mF cm2)

[0200] Turnover Frequency (TOF)

[0201] Calculation TOF was calculated using the following equation:

[0202] TOF = (J x A) / (4 x F xn)

[0203] where J is the current density (A cm2), A is the geometric surface area (0.196 cm2), F is the Faraday constant (96485 C mol-1), and n is the number of moles of active metal sites. Since no ICP measurement was performed, n was estimated as 3.6 × 10-8mol based on literature-reported values for similar catalysts at similar loading and EC SA.

[0204] Mass Activity and Specific Activity

[0205] Mass activity (MA) was defined as the geometric current density divided by the mass loading (0.2 mg cm2):

[0206] MA = J / m

[0207] Specific activity (SA) was calculated as:

[0208] SA = J / ECSA

[0209] Impedance Modeling

[0210] Nyquist plots were analyzed by fitting to an equivalent circuit model consisting of a solution resistance (Rs), charge transfer resistance (Ret), and constant phase element (CPE). The Ni-Co-P sample exhibited a lower Ret compared to its precursor, confirming enhanced conductivity and interfacial charge transport.

[0211] DFT Calculations

[0212] Spin-polarized density functional theory (DFT) calculations were performed using the Vienna Ab initio Simulation Package (VASP). The projector augmented wave (PAW) method and the Perdew-Burke-Ernzerhof (PBE) functional within GGA were used. The (210) surface of Ni1Co3P was modeled to evaluate the OER steps, including *OH, *0, and *OOH intermediates. A significant reduction in *OOH formation barrier was observed due to P doping, supported by Bader charge and d-band center analysis.

[0213] Cost-Normalized Performance

[0214] The cost-normalized activity metrics were calculated based on market prices (Ni: $0.03 / g, Co: $0.05 / g, NaH2PO2: $0.01 / g). Metrics included:

[0215] TOF / $ = TOF / total cost per mg

[0216] MA / $ = MA / cost per mg

[0217] SA / $ = SA / cost per mg These results highlight the techno-economic viability of Ni1Co3P for large-scale alkaline OER.

[0218] Characterization of Nickel-Cobalt Bimetallic Phosphide

[0219] The target electrocatalyst, a 3D Ni3Co1P phosphide network, was synthesized via thermal phosphidation of a Ni-Co bimetallic aerogel shown in FIGURE20. The Ni-Co aerogel was prepared by rapidly reducing an aqueous solution of NiCE 6EL>0 and COCI2 6H2O (Ni: Co = 3:1) with NaBEL, followed by freeze-drying to preserve its highly porous structure. To ensure uniform phosphorus incorporation while maintaining structural integrity, the as-obtained aerogel was fully immersed in deionized water and oven-dried at 85 °C, allowing controlled hydration-assisted oxidation. This oxidized intermediate was thoroughly mixed with NaH2PO2(mass ratio 1:10) and annealed at 350 °C under nitrogen flow to obtain the final Ni3Co1P phosphide material.

[0220] Scanning electron microscopy (SEM) was employed to explore the morphological transformation of aerogels into phosphides. As indicated in FIGURES 21A and 2 IB, the NisCoi aerogel is composed of a three-dimensional (3D) interconnected structure consisting of ultrathin nanoscale ligaments. This open architecture comprises micro-scale cellular porosity containing numerous voids and channels. Upon phosphidation, the surface of ligaments are made rough and, to a certain extent, coarsened because of the formation of nanoparticles, but the overall 3D structure is barely broken. The Ni3Co1P skeleton preserves its macroscopic porosity, continuity of the skeletal network, and the interpenetration among branches without any collapses, sintering, and fractures. The SEM images at different magnifications indicate that the ligament diameter, node junctions, and pore size distribution are similar before and after phosphidation. The elemental mapping of EDS and EELS in FIGURES 21D-21G and 21H-21K further verifies the Ni, Co, and P distribution homogeneity in the obtained Ni3Co1P nanonetwork. Neither elemental segregation nor phase separation was found between the analyzed regions, reflecting successful phosphorus diffusion and incorporation. The atomic ratio of Ni: Co in the phosphide was preserved with precursor composition, indicating limited loss or redistribution during annealing.

[0221] The phase transition and crystallinity of the materials are analyzed by X-ray diffraction (XRD) patterns (FIGURE 22A). The as-synthesized NisCoi aerogel exhibits clear diffraction peaks at 29 ~ 52.082°, 60.947°, and 91.73° indexed to the (111), (200), and (220) planes of FCC Ni. Especially, no Co-related peaks are seen, thus, Co does not form a distinct crystalline phase. Instead, the broadening of the Ni peaks and the total absence of Co signals indicate the formation of a Ni-Co solid solution or alloy, and Co atoms might have been embedded in the Ni lattice. This speculation is substantiated by XPS, where Ni and Co appear with partially metallic characters (Niδ+and Coδ+), and the uniform Ni: Co ratio (—3:1) with no segregation of Co oxides suggests a strong electroniccommunication between the two metals. These features are indicative of alloying and a homogeneous bimetallic network.

[0222] Upon phosphidation, there is the emergence of several sharp reflections at 29 - 47.837°, 52.433°, and 55.491°, which can be indexed to the (111), (201), and (210) planes of Ni-rich bimetallic phosphide phases (FIGURE 22B). These additional peaks suggest an elevation of the crystallinity and the appearance of additional crystal facets that were not present in the amorphous as-spun form. After phosphidation, new diffraction planes appear, indicating more available crystallographic orientations on the surface as potential active sites. In the literatures tendency to all UP based catalyst, studies that investigated the chacter of facet of UP based catalyst (001), (100) and (101) plane found that they were the most active for (HER) on account of their favorable hydrogen adsorption energies and the less energy needed for water dissociation. Thus, the new crystallographic planes created in Ni3Co1P may offer more catalytically active sites in addition to those provided, and that may contribute to the observed improved HER activity to some extent. While the reported (111), (201), and (210) planes are not directly correlated with these well-studied Ni? P facets, the higher amount of exposed crystal facets and nano-crystallinity taken together suggests a greater abundance of active sites.

[0223] Surface chemical states and atomic compositions of elements were analyzed by X-ray photoelectron spectroscopy. The survey scan (FIGURE 23 A) confirms the presence of Ni, Co, and P. In the high-resolution Ni 2p spectrum, two main peaks are observed at 855.0 eV (Ni 2p3 / 2) and 872.0 eV (Ni 2p1 / 2) that are attributed to Ni2+species in the surface oxide / hydroxide formations. A stronger shoulder peak at 852.0 eV is attributed to Niδ+, which may have originated from Ni–P bonds in the phosphide phase. The corresponding satellite peaks are also observed around 860 and 878 eV, confirming the mixed oxidation state of Ni (FIGURE 23B). The Co 2p spectrum clearly shows intense peaks at 780.4 and 795.4 eV are attributed to Co 2ps / 2 and 2p 1 / 2 signals of Co2+species, respectively, and a feature at 776.8 eV is due to Co δ+Co–P environment. Weak satellite features appear at 785.2 and 801.8 eV to support the multiplet-split oxidized cobalt (FIGURE 23C). The P 2p spectrum (FIGURE 23D) can be deconvoluted into a dominant doublet at 129.9 eV (P 2p3 / 2) and 130.7 eV (P 2p1 / 2) originating from Pδ-, which is typical for metal phosphide, and a less intense component located at -133.7 eV belonging to the surface-oxidized P-0 species. Quantitative XPS analysis gives a Ni: Co ratio that is close to, but slightly lower than, the 3: 1 precursor ratio, and EDS analysis suggests no significantloss of metal during the synthesis. The high-resolution spectra demonstrate that as-prepared Ni3Co1P is a composite material consisting of mixed Ni and Co oxidation states at the surface, a conductive phosphide core, and an ultra-thin (<1 nm) oxide shell, likely responsible for promoting water dissociation. The synergism at the metal phosphide / surface hydroxide / oxide interface may make metal phosphides good efficient for the Volmer in alkaline HER.

[0224] Surface area and pore size were determined by N2 adsorption-desorption isotherms. Both samples present type IV isotherms with a hysteresis loop, which indicates the mesoporous features. The BET surface area of Ni3Co1P is 22.96m2 / g, which is a bit higher than that of NisCoi aerogel (21.23m2 / g). This slight shift further verifies that the high-temperature phosphidation did not result in structure collapse or densification. The surface area, even with some compositional changes, reinforces the SEM conclusion that the porous framework is retained. The low relative increase might be due to the roughening of the surface by phosphidation or the presence of coarse-grained domains. Notably, while the surface area does not vary markedly, it is concluded that the improved catalytic performance (Section 2.2) is due to the intrinsic enhancement of the electronic structure and catalytic site chemistry resulting from the introduction of phosphorus.

[0225] To further elucidate the impact of phosphorus doping on the local coordination environment and electronic structure of Ni and Co atoms, we conducted simulated X-ray absorption near edge structure (XANES) spectra for both NisCoi and Ni3Co1P. As shown in FIGURE 24, both Ni and Co L-edge spectra exhibit notable energy shifts after phosphidation. In particular, the main absorption peak of the Ni Ls-edge shifts from 854.0 eV in the NisCoi alloy to 855.2 eV in Ni3Co1P, accompanied by an increase in post-edge intensity. Similarly, Co Ls-edge absorption moves from 778.7 eV to 779.5 eV upon phosphorus incorporation. These changes reflect a partial oxidation and electron redistribution near the Fermi level, consistent with the formation of Ni-P and Co-P bonds. The increased intensity and subtle broadening of the spectra also suggest enhanced hybridization between metal d-orbitals and P 3p orbitals, reinforcing the idea of strong metal-nonmetal interaction and effective electronic structure modulation. These trends are in excellent agreement with the XPS data (FIGURE 23), where the emergence of Niδ+and Coδ+states was observed. Together, the simulated XANES results provide evidence supporting the role of phosphorus in restructuring the local electronic environment, which is pivotal for hydrogen adsorption and HER kinetics.

[0226] In summary, the Ni3Co1P phosphide network retains a well-defined 3D porous architecture after phosphidation, with homogeneous elemental distribution, partial nanocrystallinity, and a chemically active surface rich in metal-P bonds. These structural and compositional characteristics contribute positively to its catalytic performance for alkaline hydrogen evolution.

[0227] Electrochemical HER Performance in Alkaline Media

[0228] The HER activity of Ni3Co1P in alkaline solution was tested in a standard three-electrode system in 1.0 M KOH solution using linear sweep voltammetry (LSV).FIGURE 24A shows the HER polarization curves of Ni3Co1P, pre-phosphated NisCoi alloy, Ni-P, Ni, and commercial 20 wt% Pt / C, respectively. Among them, Ni3Co1P has the smallest overpotential (75 mV at 10 mA cm−2), which is even better than commercial Pt / C (about 95 mV). Its hydrogen evolution activity is significantly improved, which can be attributed to the synergistic effect of bimetallic alloying and phosphorus doping.

[0229] Ni and Co alloying

[0230] Alloying of Ni and Co helps to enhance the free energy of hydrogen adsorption, while phosphating introduces active Ni-P and Co-P phases, which can mediate the adsorption and dissociation of water and the adsorption and reduction of protons. It is noteworthy that the NisCoi alloy exhibits an overpotential as low as about 190 mV at 10 mA cm−2, while the overpotential drops significantly to 75 mV after phosphating, indicating that the introduction of phosphorus plays a decisive role in the performance enhancement.

[0231] Tafel slope analysis (FIGURE 24B) further determines the kinetics of the hydrogen evolution reaction. Its Tafel slope is 101.6 mV dec⁻¹, which is not much different from the slope of Pt / C (111.9 mV dec⁻¹), indicating that the reaction conforms to the Volmer-Heyrovsky mechanism, in which the rate-limiting step is the Volmer step (water adsorption). The lower the slope, the better the reaction kinetics at more negative overpotentials. In contrast, the Tafel slopes of Ni₃Co₁, Ni-P, and Ni are 142.1, 113.6, and 144.2 mV dec⁻¹ respectively, indicating that their charge transfer kinetics are slower than that of Ni3Co1P.

[0232] To further understand their excellent catalytic performance, we determined the electrochemically active surface area (EC SA) based on the double-layer capacitance (Cdi). Ni3Co1P has a Cdl of3.35 mFcm2and an ECSA of 83.75 cm2(assuming 0.04 mF cm2for a planar electrode), which is approximately 14 times the geometric area (FIGURE 24C). This high ECSA is attributed to the 3D porous network structure retainedafter phosphating and the nanoscale phosphide grains, which provide a large number of accessible active sites for HER.

[0233] To evaluate the number and efficiency of these active sites, the turnover frequency (TOF) at 200 mV overpotential was calculated. The TOF value of Ni3Co1P is 3.56 s ', which is much higher than that of NisCoi (0.6 s '), Ni-P (1.6 s ') andNi (0.12 s ') (FIGURE 24D). This shows that the doping of P not only provides more accessible active sites (supported by ECSA), but also greatly improves the catalytic efficiency of a single site, further verifying the key role of electronic structure regulation brought by phosphorus doping in performance enhancement.

[0234] In addition, it is feasible to compare the MA and specific activity (SA) of the above materials at 200 mV. Among them, Ni3Co1P has a MA of up to 268.3 mA mg1and a SA of 16.32 mA cm2, indicating that it has excellent apparent hydrogen evolution performance and is at the leading level among non-precious metal HER catalysts (FIGURE 25 A). These findings highlight the synergistic advantages ofNi3Co1P in terms of active site density, intrinsic activity, and structure-electronic properties.

[0235] charge transfer properties by electrochemical impedance spectroscopy (EIS) were explored. Ni3Co1P has the shortest semicircle in the Nyquist plot, which means the lowest charge transfer resistance (Ret) facilitates efficient electron transfer to the active sites. The decrease in Ret is lower than that of NisCoi, Ni-P, and Ni, indicating that phosphorus plays an active role in promoting interface dynamics and conductivity.

[0236] Even after normalization based on ECSA, the performance of Ni3Co1P is still better than that of surface area, indicating that the performance improvement of Ni3Co1P is not derived from a simple increase in specific surface area, but is more likely driven by the optimization of its electronic structure and intrinsic properties of the catalytic interface. Combined with the BET data in Section 2.1, the BET surface area after phosphating increased slightly from 21.23 m 2 / g to 22.96 m 2 / g, which means that its geometry has not changed much. At the same time, the SEM image also shows that its structure is well maintained without collapse or sintering, so the performance improvement is not due to the physical area. An important performance improvement lies in the electronic and chemical structure reconstruction caused by phosphorus doping. On the one hand, the P element induces the formation of Ni-P and Co-P active phases, which makes the material surface have medium hydrogen adsorption energy, which is suitable for promoting the generation and desorption of H*; on the other hand, the introduction of Pregulates the local electron density of Ni and Co, making them partially present Ni6 and Co6+states, thereby enhancing the catalytic ability for the dissociation of water molecules (Volmer step). This electronic structure regulation is also consistent with the metal-P bond and mixed valence state revealed by XPS in Section 2.1. This inference is also supported by electrochemical impedance spectroscopy (EIS) tests. As shown in FIGURE 25B, the semicircle arc in the Nyquist plot of Ni3Co1P is the smallest, indicating that it has the lowest interfacial charge transfer resistance (Ret), faster electron transfer, and higher interfacial reaction rate, which is conducive to the acceleration of HER kinetics. In addition, the crystal structure formed after Ni3Co1P phosphating may also provide more active crystal faces. Although the detailed crystal face attribution has been discussed in Section 2.1, the improvement of electrochemical performance is closely related to these exposed crystal faces. It has been shown that specific crystal faces in Ni? P and CoP (such as (001) and (100)) have excellent HER activity, so the newly added crystal faces in Ni3Co1P may also contribute more active sites.

[0237] In summary, the high HER intrinsic activity of Ni3Co1P comes from the optimization of electronic structure (induced by P doping), the enhancement of interfacial charge transfer ability (supported by low Ret), and the exposure of more crystal face sites under a stable structure. The performance improvement is the result of the synergy of multiple factors, including structure, electronics, and kinetics.

[0238] To assess the operational durability of Ni3Co1P, long-term electrochemical stability was examined via chronopotentiometry and accelerated cycling tests. As shown in FIGURE 26 A, Ni3Co1P maintains a stable potential at 10 mAcm2for over 40 hours, with negligible degradation, outperforming Pt / C under the same conditions. Additionally, after 5000 continuous CV cycles between -0.1 V and -0.45 V (vs. RHE), the polarization curve (FIGURE 26B) remains nearly unchanged, demonstrating excellent structural and electrochemical robustness. These results affirm that Ni3Co1P possesses not only superior catalytic activity but also exceptional long-term durability in alkaline media.

[0239] To further understand the intrinsic mechanism of the excellent hydrogen evolution performance of Ni3Co1P, we carried out density functional theory (DFT) calculations in the next section to explore the role of phosphorus doping in electronic structure regulation, hydrogen adsorption optimization and reaction energy barrier reduction. These theoretical results provide important mechanistic support for experimental observations.

[0240] Economic Model and Performance-Cost Evaluation

[0241] Using standard market prices (Ni: $0.03 / g, Co: $0.05 / g, NaH2PO2: $0.01 / g), we estimate the total raw material cost of Ni3ColP to be <$0.15 / g. Combined with its high TOF (3.56 s ' at 200 mV), the catalyst achieves a cost-normalized performance of ~$0.042 / TOF, compared to ~$0.35 / TOF for Pt / C.

[0242] EXAMPLE 3: OXYGEN EVOLUTION REACTION

[0243] The present example discusses a self-supported Ni1Co3P material with a three-dimensional interconnected nanonetwork (3D INP NN) without templates and substrates. The material was prepared as discussed in Example 2.

[0244] After phosphating, the porous structure is well preserved, and the catalyst exhibits excellent OER performance with an overpotential much lower than that of IrCE. Systematic analysis shows that performance enhancement does not originate from high specific surface area but is due to phosphorus-induced electron recombination.

[0245] The present Example provides synthesis of a self-supporting, nanostructured Ni1Co3P catalyst with high-activity and stability OER performance in alkaline media. By comprehensive and surface studies, the present Example demonstrates enhanced performance arising, at least in part, from phosphorus-induced electronic rearrangements instead of induced morphological modifications. The experiments of the present Example and DFT calculations verify enhanced adsorption energetics structural and electron redistribution, and machine learning models generalize this understanding to more compositional design. The integrated design strategy provides high-performance bimetallic phosphide electrocatalysts based on data-driven electronic structure engineering.

[0246] Structural / Component Characterization

[0247] Ni1Co3P nanonetworks were prepared by a two-step method. First, Ni-Co nano bimetallic aerogels were prepared by reducing NiCl₂·6H₂O and CoCl₂·6H₂O (1:3) with NaBH₄ and then freeze-dried. After the aerogels were formed, they were soaked in deionized water and further dried at 85°C to achieve slow and uniform hydration-assisted oxidation. Subsequently, phosphating was carried out at 350°C using NaH₂PO₂ (mass ratio 1:10) under N₂ atmosphere (FIGURE 28).

[0248] SEM images (FIGURE 29A) show that the resulting NiiCos aerogel comprise a three-dimensional interconnected porous structure with nanoscale ligaments. After phosphating, Ni 1C03P still has this open network structure (FIGURE 29B), while theligament surface becomes rough and the particle size increases, indicating that the ligaments are transformed into crystalline phosphides without collapse or sintering. STEM-ADF imaging (FIGURE 29C-29E) further confirms the retention of the nanoscale hierarchical structure, while the clear grain contrast indicates the presence of partial crystallization. EDS elemental mapping (FIGURE 29G-29J) also shows thatNi, Co, and P are uniformly distributed throughout the structure, confirming the successful and uniform incorporation of P, and no phase segregation is detected.

[0249] X-ray diffraction (XRD) patterns (FIGURE 30 A) were used to analyze the crystallographic transitions and lattice parameters of the catalysts. The as-prepared NiiCos aerogel displays a broad peak around 2θ ≈ 51.9°, indicating an amorphous or poorly crystalline alloy phase. This peak position closely matches the (111) planes of facecentered cubic (FCC) Ni (PDF#04-0850, d = 2.034 A) and Co (PDF#15-0806, d = 2.0467 A), suggesting the formation of a Ni-Co solid solution with alloying-induced peak broadening due to lattice distortion. After phosphating, several sharp peaks emerge in the XRD pattern (FIGURE 30B), corresponding to the (111), (201), and (210) reflections of bimetallic phosphide phases. These peaks are consistent with standard patterns of orthorhombic CoP (PDF#29-0497), with characteristic d-spacings of 2.008 A [(210)], 1.962 A [(112)], and 1.889 A [(211)]. The transition from a broad alloy peak to well-defined crystalline phosphide peaks confirms the successful phase transformation and crystallization induced by phosphorus doping. Importantly, the measured d-spacing values derived from the Bragg equation align well with the standard data, further validating the structural evolution. This sets the foundation for high-resolution transmission electron microscopy (HRTEM) imaging to directly observe the atomic lattice fringes directly, enabling further validation of the crystalline phase and local structure. By correlating these XRD-derived d-spacings with HRTEM lattice measurements, we aim to confirm the formation of specific catalytically active facets and their relation to electrocatalytic performance.

[0250] The surface electronic modifications are also confirmed by XPS measurements. In the high-resolution Ni 2p spectrum, the peaks at 851 eV and 856 eV should be assigned to Niδ (metal-P bonds) and Ni 2+(surface oxidation), respectively (FIGURE 29C). Co 2p has Coδ and Co2+peaks at 778.5 eV, as well as a broad Co2+peak (FIGURE 29D). In the P 2p spectrum, the main doublet at 129.5 eV corresponds to metal-P bonds, and the minor peak at about 133.5 eV is assigned to oxidized phosphate species(FIGURE 29E). It is noted that the Ni: Co ratio determined by XPS spectroscopy remains roughly constant at around 1:3, consistent with the EDS data and the precursor composition, thus confirming the integrity of the composition.

[0251] The porosity was determined by N2 adsorption-desorption isotherms (FIGURE 29F). Both NiiCos and Ni1Co3P have type IV isotherms and H3-type hysteresis loops, indicating mesoporosity. In both cases, the BET surface area increases from 20.13 m2 / g (NiiCos) to 22.05 m2 / g (Ni1Co3P), while the total pore volume and average pore size remain almost unchanged. The good consistency of SEM, STEM, BET, and XRD results indicates that the structural evolution is mainly caused by phase and bond changes rather than textural transformations, which suggests that the improvement in catalytic activity should be due to electronic structure reconstruction rather than surface area enrichment.

[0252] Electrocatalytic OER Performance

[0253] The OER activity of Ni1Co3P was tested in 1.0 M KOH solution and compared with NiiCos, Ni-P, and commercial IrCE As shown in FIGURE 31 A, Ni1Co3P shows the lowest overpotential of 208 mV at 10 mA cm2current density, which is better than IrO? (265 mV).

[0254] The Tafel cross section (FIGURE 3 IB) shows that the slope of Ni1Co3P is 58.6 mV dec which is significantly smaller than that of the control sample, indicating faster reaction kinetics. This rate is consistent with the theoretical estimate of the ratelimiting OOH formation step described further herein. The improvement in kinetics is attributed to the optimization of adsorption energy and charge transfer kinetics brought about by phosphorus doping.

[0255] To investigate the intrinsic activity, the ECSA was extracted from the double layer capacitance (Cai). After normalization by ECSA, the polarization curve of Ni1Co3P is still at a higher level than the other polarization curves, indicating that Ni1Co3P has higher single-site activity. These results are consistent with the BET data, indicating that the increase in surface area is not the main factor for the improvement of activity.

[0256] The mass activity (MA) and related activity (SA) were also calculated at a constant overpotential of 300 mV. In present Example, the MA and SA of Ni1Co3P are 560.23 mA mg1and 0.716 mA cm2, respectively, which are much higher Ni, NiP, and NiiCos. These values highlight the excellent utilization efficiency of the catalyst and its excellent scalability for high current density electrolysis.

[0257] The electrochemical impedance spectra (EIS) of these samples are shown in FIGURE 32A, from which it can be clearly seen that Ni1Co3P has the smallest Nyquist plot semicircle, indicating the lowest interfacial charge transfer resistance (Ret). This is consistent with the higher crystallinity and enhanced conductivity shown by XRD and XPS measurements. The high structure-electrochemical correlation verifies the ability of the phosphide phase to promote fast electron transfer and interfacial dynamics.

[0258] The catalyst also demonstrates excellent long-term durability. Ni1Co3P exhibits a stable chronopotentiometric response over 40 hours at a constant current density of 10 mA cm2without noticeable potential drift (FIGURE 32B). Moreover, after 5000 continuous cyclic voltammetry (CV) cycles, Ni1Co3P retains its catalytic activity with negligible performance loss, underscoring its outstanding electrochemical stability (FIGURE 32C). This durability is attributed to its robust, highly covalent metal-phosphorus lattice and uniform microstructure, which effectively resists corrosion and preserves the integrity of active catalytic sites.

[0259] Unless stated otherwise, experimental hypotheses or forward-looking models and statements are not intended to be binding on the applicant or exhaustive of the range of possible experimental hypotheses or forward-looking models and statements, but rather are intended to be illustrative, non-limiting examples for aiding those in the art in the understanding and practice of elements of the disclosure.

[0260] As used herein and unless otherwise indicated, the terms “a” and “an” are taken to mean “one”, “at least one” or “one or more”. Unless otherwise required by context, singular terms used herein shall include pluralities and plural terms shall include the singular.

[0261] Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

[0262] Unless the context clearly requires otherwise, the phrase “consisting essentially of’ limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s) of the claim.

[0263] Unless the context clearly requires otherwise, the phrase “consisting of’ excludes any element, step, or ingredient not specified.

[0264] If an element is described or claimed herein such that it “comprises” a feature, that description or claim also includes embodiments wherein the element “consists essentially of’ and embodiments wherein the element “consists of’ the feature, unless something else is specifically stated to the contrary.

[0265] Unless otherwise stated or the context clearly requires otherwise, methods of the disclosure can be performed, in whole or in part, in any order of steps, including steps that are performed subsequently, in parallel, and in combination. In addition, methods can be performed, in whole or in part, by humans optionally assisted by one or more machines such as one or more computational devices or systems (e.g., computer(s)). In at least some instances, methods can be performed by one or more humans with little or no substantive assistance by one or more machines. In at least some other instances, methods can be performed by one or more humans with substantive assistance by one or more machines, and in at least some instances, one or more machines can perform methods autonomously or semi-autonomously.

[0266] Unless otherwise indicated, all numbers expressing quantities of components, molecular weights, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless otherwise indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that can vary depending upon the desired properties sought to be obtained by the present disclosure. At the very least, and not as an attempt to limit the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0267] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. All numerical values, however, inherently contain a range necessarily resulting from the standard deviation found in their respective testing measurements.

[0268] The term “about” means plus or minus 5% of the stated value.

[0269] All headings are for the convenience of the reader and should not be used to limit the meaning of the text that follows the heading, unless so specified.

[0270] All of the references cited herein are incorporated by reference. Aspects of the disclosure can be modified, if necessary, to employ the systems, functions, andconcepts of the cited references and disclosure to provide yet further embodiments of the disclosure. These and other changes can be made to the disclosure in light of the detailed description.

[0271] The above description of illustrated embodiments of the present disclosure, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.

[0272] These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.

Claims

CLAIMSThe embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A catalyst composition comprising:a nanofoam comprising a plurality of intertwined nanowires comprising two or more metals.

2. The catalyst composition of Claim 1, wherein the nanofoam comprises a three-dimensional interconnected nanonetwork comprising the plurality of intertwined nanowires.

3. The catalyst composition of any one of Claims 1 and 2, wherein the nanofoam is an aerogel comprising the plurality of intertwined nanowires.

4. The catalyst composition of any one of Claims 1-3, wherein the nanofoam is self-supported.

5. The catalyst composition of Claim 4, wherein the catalyst composition does not comprise a substrate supporting the nanofoam.

6. The catalyst composition of any one of Claims 1-5, wherein the plurality of intertwined nanowires comprises an alloy or solid solution of the two or more metals.

7. The catalyst composition of any one of Claims 1-6, wherein the plurality of intertwined nanowires comprises a sintered mixture of the two or more metals.

8. The catalyst composition of any one of Claims 1-6, wherein the plurality of intertwined nanowires comprises an un-sintered mixture of the two or more metals.

9. The catalyst composition of any one of Claims 1-8, wherein an average pore size of the nanofoam is in a range of about 15 nm to about 80 nm.

10. The catalyst composition of any one of Claims 1-9, wherein an average diameter of nanowires of the plurality of nanowires is in a range of about 20 nm to about11. The catalyst composition of any one of Claims 1-10, wherein a Brunauer-Emmett-Teller (BET) surface area of the nanofoam is in a range of about 5 m2 / g to about 25 m2 / g.

12. The catalyst composition of any one of Claims 1-11, wherein an electrochemically active surface area (ECSA) of the nanofoam is in a range of about 70 cm2 / g to about 90 cm2 / g.

13. The catalyst composition of any one of Claims 1-12, wherein the two or more metals are selected from group consisting of Ni, Sn, and Co.

14. The catalyst composition of Claim 13, wherein the two or more metals comprise Ni and Sn.

15. The catalyst composition of Claim 14, wherein a molar ratio of Ni: Sn is in a range of about 1: 1 to about 5:1.

16. The catalyst composition of Claim 14, wherein the plurality of intertwined nanowires comprises a compound NixSny, wherein x is an integer having a value chosen from 4 and 3, and wherein y is an integer having a value chosen from 1-4.

17. The catalyst composition of Claim 14, wherein the plurality of intertwined nanowires comprise compounds selected from the group consisting of Ni3Sn4, Ni3Sn, Ni3Sn2, Ni4Sn3, and combinations thereof.

18. The catalyst composition of Claim 13, wherein the two or more metals comprise Ni and Co.

19. The catalyst composition of Claim 18, wherein a molar ratio of Ni: Co is in a range of about 1:3 to about 3:1.

20. The catalyst composition of any one of Claims 18 and 19, wherein the plurality of intertwined nanowires comprises NiCo3.

21. The catalyst composition of any one of Claims 1-20, wherein the plurality of intertwined nanowires comprises a phosphide compound of the two or more metals.

22. The catalyst composition of Claim 21, wherein the plurality of intertwined nanowires comprises NiCo3P.

23. The catalyst composition of any one of Claims 21 and 22, wherein nanowires of the plurality of intertwined nanowires comprise surfaces comprising metal-P bonds.

24. The catalyst composition of any one of Claims 21-23, wherein nanowires of the plurality of intertwined nanowires comprise conductive phosphide cores.

25. A method of making a bimetallic nanofoam catalyst composition, the method comprising:introducing a reducing agent to a solution comprising a first metal source and a second metal source to provide a bimetallic nanofoam comprising a plurality of intertwined nanowires defining a three-dimensional interconnected nanonetwork.

26. The method of Claim 25, wherein the first metal source is selected from NiCl2and Ni(NO3)2and the second metal source is selected from CoCl2and SnCl2.

27. The method of any one of Claims 25 and 26, wherein the reducing agent comprises NaBH4.

28. The method of any one of Claims 25-27, further comprising removing water from the bimetallic nanofoam, thereby retaining a three-dimensional structure the three-dimensional interconnected nanonetwork.

29. The method of Claim 28, wherein removing the water from the bimetallic nanofoam comprises freeze drying the bimetallic nanofoam.

30. The method of Claim 29, further comprising annealing a mixture of the dried bimetallic nanofoam and a phosphorus source in an inert atmosphere to provide a bimetallic phosphide nanofoam.

31. The method of Claim 30, wherein the phosphorus source comprises NaH2PO2.

32. The method of any one of Claims 30 and 31, wherein a mass ratio of the dried bimetallic nanofoam and the phosphorus source is in a range of about 1:20 to about 1:5.

33. A method of catalyzing a reaction, the method comprising: contacting a catalytic substrate with a catalyst composition according to any one of Claims 1-24, thereby catalyzing a reaction of the substrate.

34. The method of Claim 33, wherein the catalytic substrate comprises water, and wherein the reaction is electrolysis of water.

35. The method of Claim 34, wherein the water is salt water.

36. The method of any one of Claims 34 and 35, wherein the catalyst composition has an overpotential in a range of about 70 mV and about 300 mV measured at 10 mA / cm2.

37. The method of any one of Claims 34-36, wherein the mass activity of the catalyst composition is in a range of about 200 mA / mg to about 600 mA / mg.

38. The method of any one of Claims 34-37, wherein the specific activity of the catalyst composition is in a range of about 0.5 mA / cm2to about 0.8 mA / cm2.

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